1. Field of the Invention
This invention relates to a photoconductive member having sensitivity to electromagnetic waves such as light (herein used in a broad sense, including ultraviolet rays, visible light, infrared rays, X-rays and gamma-rays).
2. Description of the Prior Art
Photoconductive materials, which constitute image forming members for electrophotography in solid state image pick-up devices or in the field of image formation, or photoconductive layers in reading devices, are required to have a high sensitivity, a high SN ratio [Photocurrent (I.sub.p)/(I.sub.d)], absorption spectral characteristics matched with those of electromagnetic waves to be irradiated, a rapid response to light, a desired dark resistance value as well as no harm to human bodies during use. Further, in a solid state image pick-up device, it is also required that the residual image should easily be treated within a predetermined time. Particularly, in case of an image forming member for electrophotography to be assembled in an electrophotographic apparatus to be used in an office as a business machine, the aforesaid safety characteristic is very important.
From the standpoint as mentioned above, amorphous silicon (hereinafter referred to as a-Si) has recently attracted attention as a photoconductive material. For example, German OLS Nos. 2746967 and 2855718 disclose applications of a-Si for use in image forming members for electrophotography, and German OLS No. 2933411 discloses an application of a-Si for use in a photoelectric reader.
However, under the present situation, the photoconductive members of the prior art having photoconductive layers constituted of a-Si are further required to be improved in a balance of overall characteristics including electrical, optical and photoconductive characteristics such as dark resistance, photosensitivity and response to light, etc., and environmental characteristics during use such as humidity resistance, and further stability with lapse of time.
For instance, when the above photoconductive member is applied to an image forming member for electrophotography, residual potential is frequently observed to remain during use thereof if improvements to higher photosensitivity and higher dark resistance are intended at the same time. When such a photoconductive member is repeatedly used for a long time, there will be caused various inconveniences such as accumulation of fatigue by repeated uses or so called ghost phenomenon wherein residual images are formed.
Further, according to a large number of experiments by the present inventors, a-Si as the material constituting the photoconductive layer of an image forming member for electrophotography, while it has a number of advantages, as compared with inorganic photoconductive materials such as Se, CdS, ZnO or organic photoconductive materials such as PVCz or TNF of prior arts, is also found to have problems to be solved. Namely, when charging treatment is applied for formation of electrostatic images on the photoconductive layer of an image forming member for electrophotography having a photoconductive member constituted of a mono-layer of a-Si which has been endowed with characteristics for use in a solar battery of prior art, dark decay is markedly rapid, whereby it is difficult to apply a conventional electrophotographic process. Moreover, this tendency is further pronounced under a humid atmosphere to such an extent in some cases that no charge is retained before development time.
Further, a-Si materials may contain as constituent atoms hydrogen atoms or halogen atoms such as fluorine atoms, chlorine atoms, etc. for improving their electrical, photoconductive characteristics, boron atoms, phosphorus atoms, etc. for controlling the electroconduction type as well as other atoms for improving other characteristics. Depending on the manner in which these constituent atoms are contained, there may sometimes be caused problems with respect to electrical or photoconductive characteristics of the layer formed.
Especially, at the interface between the layers adjacent to each other, dangling bonds are liable to be formed in manufacturing process and complicated bendings are also liable to occur in energy bands. For this reason, the problems of behaviors of the charges or stability of the structure become very important, and controlling of this part is not seldom a key for having the photoconductive member exhibit its function as desired.
Also, when a-Si type photoconductive member is prepared by a method generally known in the art, various problems are caused in many cases such as insufficient life of the photocarriers generated by light irradiation of the photoconductive layer formed throughout said layer or insufficient impedance of charges injected from the support side. Accordingly, while attempting to improve the characteristics of a-Si material per se on one hand, it is also required to make efforts to obtain desired electrical and optical characteristics as mentioned above in designing of the photoconductive member on the other.
In view of the above points, the present invention contemplates the achievement obtained as a result of extensive studies made comprehensively from the standpoints of applicability and utility of a-Si as a photoconductive member for image forming members for electrophotography, solid stage image pick-up devices, reading devices, etc. It has now been found that a photoconductive member having a layer constitution comprising a photoconductive layer exhibiting photoconductivity, which is constituted of so called hydrogenated amorphous silicon, or halogen-containing hydrogenated amorphous silicon which is an amorphous material containing at least one of a hydrogen atom (H) and a halogen atom (X) in a matrix of a-Si, especially silicon atoms [hereinafter referred to comprehensively as a-Si(H,X)], said photoconductive member being prepared by designing so as to have a specific structure as hereinafter described, is found to exhibit not only practically extremely excellent characteristics but also surpass the photoconductive members of the prior art in substantially all respects, especially having markedly excellent characteristics as a photoconductive member for electrophotography.